Modified sepiolite heavy metal adsorption material and preparation method thereof
Technical Field
The invention belongs to the technical field of environmental pollution remediation and environmental engineering materials, and particularly relates to modified sepiolite and a preparation method thereof, which can be used for efficiently adsorbing heavy metals of cadmium and arsenic in sewage and passivating soil simultaneously.
Background
With the development of industrial production, large amounts of wastewater containing heavy metals are discharged into the environment. Heavy metals have the characteristics of being non-biodegradable but easily absorbed by organisms, and once entering the environment, the heavy metals threaten the growth of animals and plants and the health of human bodies. Therefore, the removal of heavy metal ions in water body draws wide attention of scholars at home and abroad.
The conventional technologies for treating heavy metal pollution in water mainly comprise a chemical precipitation method, an ion exchange method, an electrolysis method, an oxidation-reduction method, a membrane separation technology, a biological purification method, an adsorption method and the like, wherein the adsorption method is highly emphasized by the characteristics of good treatment effect, simple operation and the like.
The core of the technology for treating heavy metal wastewater by an adsorption method is a material for adsorption, and the material mainly comprises natural minerals such as bentonite, montmorillonite, sepiolite and iron-manganese ore, industrial wastes such as steel slag, fly ash and red mud, biological wastes such as sawdust, straw, biochar and activated sludge, and novel materials such as ion exchange resin and polyethylene high polymer material. In recent years, porous particle materials gradually enter the research field of heavy metal pollution adsorption of water, and not only have the characteristics of quick adsorption and desorption, but also are easy to separate and recycle. The pore wall structure on the surface of the material can be changed by means of modification and the like, so that the surface area of the adsorption material is increased, and the adsorption effect of the material on heavy metals is further improved. Therefore, the porous particle heavy metal adsorbent with excellent performance is prepared by using materials with wide sources and low price, and has wide development prospect.
Sepiolite is a natural mineral with stable property, wide source, economy and easy obtaining. In recent years, the sepiolite or modified sepiolite has better effect on treating the heavy metal wastewater, but mainly focuses on improving the heavy metal cations such as Cr6+、Pb2 +、Cu2+、Cd2+、Hg2+、Ni2+And the like. Arsenic is a carcinogen, usually as AsO3 3-Or AsO5 3-The anionic form exists. Many industrial wastewaters contain Cd in addition to2+The heavy metal cations also contain arsenic. Therefore, the research can simultaneously remove heavy metal cation Cd in the water body2+And anionic AsO3 3-Or AsO5 3-The technology of (2) has very important significance. The sepiolite is modified by the ferrous sulfate and the potassium permanganate, so that the adsorption sites of the sepiolite surface for cadmium and arsenic are increased, and the removal efficiency of the cadmium and arsenic is greatly improved. In addition, the modified sepiolite prepared by the method can also obviously reduce the concentration of cadmium and arsenic in the pore water of the composite polluted soil, and has the effect of passivating the cadmium and the arsenic in the soil.
The modification of sepiolite and its application in waste water treatment have not been doneFew reports and patents. For example, sepiolite is subjected to cellulose modification to adsorb organic pollutants (application No. 201310262836), the sepiolite is subjected to cellulose and iron salt modification to adsorb phenol and heavy metal pollutants (application No. 201610068846), the sepiolite is subjected to nano-iron modification to degrade organic pollutants (application No. 201210118344), and waste water is modified by microwave reaction of a mixture of sepiolite and kaolin, cellulose and ferric chloride (application No. 201710458501). The modified sepiolite prepared above mainly targets organic pollutants, while basically heating or special devices (such as microwaves) are required, and the cost is relatively high. There are reports in the literature that iron-modified sepiolite can improve arsenic adsorption ((R))
et al, 2014), it has also been reported in the literature that iron-modified sepiolite enhances the removal of Cu, Cd and Zn from solution (Bahabadi et al, 2017). But reports of adsorbing heavy metals after carrying out iron and manganese modification on sepiolite are not found. Compared with iron modification, iron and manganese modification not only utilizes Fe-OH formed by iron to enhance the adsorption of cadmium and arsenic, but also can further enhance the adsorption efficiency of cadmium and arsenic by utilizing the oxidation and adsorption effects of manganese oxide on arsenic. The comparative experiment proves that the ferrous sulfate and potassium permanganate modified sepiolite with the same proportion has better adsorption effect on cadmium and arsenic in the solution than the ferrous sulfate modified sepiolite, and the ferro-manganese modification has synergistic effect.
Disclosure of Invention
The invention aims to provide a modified sepiolite heavy metal adsorption material, which is prepared by adding a mixed solution of ferrous sulfate and potassium permanganate to modify sepiolite, filtering, washing and drying, so that the surface area and adsorption sites of the adsorption material are effectively improved, and the modified sepiolite heavy metal adsorption material has a good adsorption effect on heavy metal cadmium and arsenic.
The invention also aims to provide a preparation method of the modified sepiolite heavy metal adsorption material, which is simple, low in consumption, easy to operate and good in industrial application prospect.
In order to achieve the purpose, the invention adopts the following technical scheme:
a modified sepiolite heavy metal adsorption material is prepared by loading a binary compound of iron and manganese on natural sepiolite, wherein the preparation raw materials comprise 20 parts by weight of natural sepiolite, 1-6 parts by weight of iron and 1-6 parts by weight of manganese, the iron salt is ferrous sulfate, and the manganese salt is potassium permanganate.
Preferably, the raw materials for preparing the adsorbing material comprise 20 parts by weight of natural sepiolite, 3-6 parts by weight of iron and 1-2 parts by weight of manganese.
Preferably, the raw materials for preparing the adsorbing material comprise 20 parts by weight of natural sepiolite, 6 parts by weight of iron and 2 parts by weight of manganese.
Preferably, the raw materials for preparing the adsorbing material comprise 20 parts by weight of natural sepiolite, 3 parts by weight of iron and 1 part by weight of manganese.
The preparation method of the modified sepiolite heavy metal adsorption material comprises the following steps:
(1) taking natural sepiolite as a raw material, drying, crushing and sieving;
(2) weighing ferrous sulfate and potassium permanganate according to a certain proportion, dissolving in water, mixing uniformly, adjusting the pH value of the solution to 6-9, adding sepiolite, stirring uniformly, and standing to obtain slurry;
(3) and (3) taking out the mixed slurry obtained in the step (2), repeatedly washing and filtering until the washing liquid is clear, drying the solid and grinding.
The technical principle of the invention is as follows: the sepiolite is a fibrous porous magnesium-containing silicate, has two layers of silicon-oxygen tetrahedrons, one layer is a magnesium-oxygen octahedron, and water molecules and exchangeable cations exist in alternately arranged pore passages of an upper layer and a lower layer, so the sepiolite has a large specific surface area and is rich in heavy metal adsorption sites. Fe-OH is generated on the surface of the sepiolite by loading iron, so that the adsorption of cadmium (Fe-O-Cd) and arsenic (Fe-As) can be enhanced; manganese oxide pair As5+Has good adsorption effect, and the manganese oxide can adsorb As in solution3+By oxidation to As5+Further improving the adsorption efficiency of arsenic. Therefore, the sepiolite is modified by adding ferrous sulfate and potassium permanganate, and the adsorption performance of the sepiolite on cadmium and arsenic can be enhanced.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) the preparation method and the preparation conditions of the invention are simple, the related reaction temperature only needs normal temperature, the energy consumption is less, and the Fe on the surface of the material is less3+Fe — OH is generally formed to be charged by proton dissociation or association, thereby adsorbing a negatively charged functional group due to electrostatic attraction; after the sepiolite is modified, the surface area is increased, the adsorption sites are greatly improved, and the adsorption capacity to heavy metals is increased.
(2) The invention prepares the material manganese ion and As3+Oxidation-reduction reaction occurs, and a new adsorption surface is generated in the process, which is favorable for adsorbing As generated by oxidation5+Thereby improving the adsorption efficiency of arsenic.
(3) The adsorption efficiency of the iron-manganese modified sepiolite on cadmium and arsenic is respectively as high as 92% and 93% (see figure 1), wherein the optimal adsorption scheme is FMP (6:2: 20). Considering the adsorption efficiency and economic benefit comprehensively, a suboptimal scheme FMP (3:1:20) is selected, and the adsorption efficiency of the suboptimal scheme FMP on cadmium and arsenic is 81% and 90%, respectively. The addition of FMP (3:1:20) material to cadmium and arsenic contaminated soil reduced the cadmium content in the soil pore water by 77% and 96% compared to the control (see FIG. 2) and the arsenic content by 71% and 55% compared to the control (see FIG. 3).
(4) The method has the advantages of simple operation, low energy consumption and environmental protection, and the obtained manganese-iron modified sepiolite has wide prospect, can be applied to treatment of heavy metal sewage, and can also be applied to remediation of heavy metal contaminated soil.
Drawings
Fig. 1 shows the results of the determination of the heavy metal adsorption performance of the modified sepiolite of the present invention (Sep and FMP in the abscissa refer to sepiolite and ferromanganese modified sepiolite, respectively).
Fig. 2 is a graph showing the measurement result of cadmium in the pore water of the soil 10 days after the ferro-manganese modified sepiolite prepared in example 1 is added to the soil.
Fig. 3 is a graph showing the measurement results of arsenic in the pore water of soil after the ferro-manganese modified sepiolite prepared in example 1 is added to the soil for 10 days.
Fig. 4 shows the results of the heavy metal adsorption performance of iron-modified sepiolite and iron-manganese-modified sepiolite with different valence states (Sep means sepiolite, FP (0) means zero-valent iron-modified sepiolite, FP (2+) means ferrous sulfate-modified sepiolite, FP (3+) means ferric nitrate-modified sepiolite, and FMP (2+) means iron-manganese-modified sepiolite).
FIG. 5 shows the results of the determination of heavy metal adsorption performance of various iron and manganese modified sepiolites (Sep means sepiolite, FMP (2+) means ferrous sulfate and potassium permanganate modified sepiolites, and FMP (3+) means ferric nitrate and potassium permanganate modified sepiolites).
Fig. 6 shows the results of the determination of the heavy metal adsorption performance of the iron-manganese modified clay minerals (FMP refers to ferrous sulfate and potassium permanganate modified sepiolite, FMB refers to ferrous sulfate and potassium permanganate modified bentonite, and FMS refers to ferrous sulfate and potassium permanganate modified diatomite).
FIG. 7 is a process and technical route flow diagram of the present invention.
Detailed Description
Example 1(Fe: Mn: Sep ═ 3:1:20)
A preparation method of a modified sepiolite heavy metal adsorption material comprises the following steps:
(1) taking sepiolite raw materials, drying, crushing, and sieving by a 100-mesh sieve;
(2) weighing 149g of ferrous sulfate heptahydrate and 28g of potassium permanganate, putting the ferrous sulfate heptahydrate and the potassium permanganate into a container, adding water for dissolving to prepare a mixed solution of potassium permanganate and ferrous sulfate, adjusting the pH value to 7.5, adding water to 2000ml, accurately weighing 200g of sepiolite, adding the sepiolite into the mixed solution of the ferrous sulfate and the potassium permanganate, stirring uniformly for half an hour, and standing for 24 hours to prepare a slurry;
(3) taking out the mixed slurry obtained in the step (2), adding water for washing, repeatedly washing and filtering to wash off Fe on the surface of the material2 +、Mn2+Filtering until the water washing liquid is clear, drying the solid at 105 ℃, drying the material, and grinding to obtain the iron-manganese modified sepiolite;
determining the effect of the modified sepiolite on adsorbing cadmium and arsenic in the wastewater: firstly, 100mg/L Cd is prepared2+And 100mg/L As3+Adding sepiolite and modified sepiolite into the solution at solid-to-liquid ratio of 1:100, shaking for 12 hr, collecting supernatant, and treatingWherein Cd2+The concentration was measured by atomic absorption spectrophotometer, As3+The concentration is measured by an atomic fluorescence spectrophotometer, and the adsorption rate of the modified sepiolite adsorbent to heavy metal is calculated according to the concentration difference of the heavy metal ions in the working solution before and after adsorption. As shown in fig. 1, under the laboratory conditions, the efficiency of adsorbing cadmium is 81% and the efficiency of adsorbing arsenic is 90% after 12 hours, so that the material prepared in this embodiment achieves a good removal effect on cadmium and arsenic in water.
Determining the effects of cadmium and arsenic in the modified sepiolite passivated soil: soil (Cd is 1.44mg/L, As is 44.0mg/L) of a certain polluted rice field soil (Cd is 1.44mg/L, As is 44.0mg/L) from Liuyang county of Hunan province is dried in the sun and sieved by a 20-mesh sieve, and then the soil is filled into pots, and each pot is filled with 400g of soil. The material prepared in this example was added to the contaminated soil at 0.5% and 1.5% doses, and water was added to bring the water level 2cm above the soil. And after flooding for 10 days, taking the soil pore water by using a pore water sampler, and measuring the concentrations of cadmium and arsenic in the soil pore water. The cadmium concentration is measured by a graphite furnace spectrophotometry method, and the arsenic concentration is measured by an atomic fluorescence spectrophotometry method. The material prepared by the embodiment is added into the soil compositely polluted by cadmium and arsenic according to the dosage of 0.5 percent and 1.5 percent, and the content of cadmium and arsenic in the soil pore water is obviously reduced after the soil is flooded for 10 days. The cadmium content is reduced by 77% and 96% compared with the control (see figure 2), and the arsenic content is reduced by 71% and 55% compared with the control (see figure 3), so that the cadmium and arsenic in the soil can be passivated simultaneously, and the aim of reducing the activity of the cadmium and arsenic in the soil is fulfilled.
Example 2(Fe: Mn: Sep ═ 6:2:20)
A preparation method of a modified sepiolite heavy metal adsorption material comprises the following steps:
(1) taking sepiolite raw materials, drying, crushing, and sieving by a 100-mesh sieve;
(2) weighing 298g of ferrous sulfate heptahydrate and 56g of potassium permanganate, putting the weighed materials into a container, adding water to dissolve the materials to prepare a mixed solution of potassium permanganate and ferrous sulfate, adjusting the pH value to 7.5, adding water to 2000mL, accurately weighing 200g of sepiolite, adding the sepiolite into the mixed solution of the ferrous sulfate and the potassium permanganate, stirring uniformly for half an hour, and standing for 24 hours to obtain a slurry;
(3) and (3) taking out the mixed slurry obtained in the step (2), adding water for washing, repeatedly washing and filtering, filtering until the washing liquid is clear, drying the solid at 105 ℃, drying the material, and grinding to obtain the iron-manganese modified sepiolite.
Under the laboratory conditions, the cadmium adsorption efficiency of the material prepared by the embodiment is 92% (see fig. 1) and the arsenic adsorption efficiency of the material is 93% (see fig. 1) after 12 hours, so that the cadmium and arsenic removal effect of water can be achieved.
Example 3(Fe: Mn: Sep ═ 2:6:20)
A preparation method of a modified sepiolite heavy metal adsorption material comprises the following steps:
(1) taking sepiolite raw materials, drying, crushing, and sieving by a 100-mesh sieve;
(2) weighing 99g of ferrous sulfate heptahydrate and 168g of potassium permanganate, putting the weighed materials into a container, adding water to dissolve the materials to prepare a mixed solution of potassium permanganate and ferrous sulfate, adjusting the pH value to 7.5, accurately weighing 200g of sepiolite, adding the sepiolite into the mixed solution of the ferrous sulfate and the potassium permanganate, stirring uniformly for half an hour, and standing for 24 hours to prepare a slurry;
(3) and (3) taking out the mixed slurry obtained in the step (2), adding water for washing, repeatedly washing and filtering, filtering until the washing liquid is clear, drying the solid at 105 ℃, drying the material, and grinding to obtain the iron-manganese modified sepiolite.
Under the laboratory conditions, the cadmium adsorption efficiency of the material prepared by the embodiment is 81% (see fig. 1) and the arsenic adsorption efficiency of the material is 84% (see fig. 1) after 12 hours, so that the cadmium and arsenic removal effect of water can be achieved.
Example 4(Fe: Mn: Sep ═ 1:3:20)
A preparation method of a modified sepiolite heavy metal adsorption material comprises the following steps:
(1) taking sepiolite raw materials, drying, crushing, and sieving by a 100-mesh sieve;
(2) weighing 49.5g of ferrous sulfate heptahydrate and 84g of potassium permanganate, putting the weighed materials into a container, adding water to dissolve the materials to prepare a mixed solution of potassium permanganate and ferrous sulfate, adjusting the pH value to 7.5, adding water to 2000mL, accurately weighing 200g of sepiolite, adding the sepiolite into the mixed solution of the ferrous sulfate and the potassium permanganate, stirring uniformly for half an hour, and standing for 24 hours to obtain a slurry;
(3) and (3) taking out the mixed slurry obtained in the step (2), adding water for washing, repeatedly washing and filtering, filtering until the washing liquid is clear, drying the solid at 105 ℃, drying the material, and grinding to obtain the iron-manganese modified sepiolite.
Under the laboratory conditions, the cadmium adsorption efficiency of the material prepared by the embodiment is 64% (see fig. 1) after 12 hours, and the arsenic adsorption efficiency is 73% (see fig. 1), so that the cadmium and arsenic removal effect in water can be achieved.
Example 5 comparison of effects of adsorbing cadmium and arsenic of iron-modified sepiolite with different valence states and iron-manganese-modified sepiolite
(1) The preparation method of the ferrous iron modified sepiolite comprises the following steps: weighing 149g of ferrous sulfate heptahydrate, putting the ferrous sulfate heptahydrate into a container, adding water for dissolving to prepare a ferrous sulfate solution, adjusting the pH to 7.5, adding water to 2000ml, accurately weighing 200g of sepiolite, adding the sepiolite into the ferrous sulfate solution, stirring uniformly for half an hour, and standing for 24 hours to obtain a slurry; then taking out the slurry, adding water for washing, repeatedly washing and filtering to wash off Fe on the surface of the material2+. Filtering until the water washing liquid is clear, and drying the solid at 105 ℃. The material is dried and ground to obtain the iron modified sepiolite FP (2 +).
(2) The preparation method of the ferric iron modified sepiolite comprises the following steps: 216g of ferric nitrate nonahydrate is weighed and placed in a container to be dissolved by water, and other steps are carried out to obtain the iron modified sepiolite FP (3+) after the material in the step (1) is dried and ground.
(3) The preparation method of the 0-valent iron modified sepiolite comprises the following steps: placing 20g sepiolite in 500ml ethanol and water
(V/V ═ 4:1) to the mixture, ultrasonic treatment was carried out for 10min, then the pH of the solution was adjusted to 4 with 0.1mol/L nitric acid, 14.9g of ferrous sulfate heptahydrate was added, ultrasonic treatment was carried out again for 10min, and 1mol/LKBH was added dropwise under argon gas filling4100ml, stirring for 20min, vacuum filtering, washing with ethanol for several times, preparing zero-valent iron, drying in a freeze drier (-50 ℃), drying the material, and grinding to obtain iron-modified sepiolite FP (0).
(4) The preparation method of the iron-manganese modified sepiolite comprises the following steps: as in example 1, FMP (2+) was used.
The experimental method for the cadmium and arsenic adsorption effect of the iron-modified sepiolite and the iron-manganese-modified sepiolite with different valence states is the same as that in the embodiment 1, the cadmium and arsenic adsorption effect of the material prepared in the embodiment under the laboratory condition is shown in fig. 4, the cadmium adsorption efficiency of the iron-modified sepiolite FP (0) after 12 hours is 18%, and the arsenic adsorption efficiency is 95%; the efficiency of adsorbing cadmium of the iron modified sepiolite FP (2+) after 12 hours is 65 percent, and the efficiency of adsorbing arsenic is 80 percent; the efficiency of adsorbing cadmium of the iron modified sepiolite FP (3+) after 12 hours is 56 percent, and the efficiency of adsorbing arsenic is 76 percent; the efficiency of adsorbing cadmium of the iron-manganese modified sepiolite after 12 hours is 81 percent, and the efficiency of adsorbing arsenic is 90 percent. Comprehensively considering the effect of adsorbing cadmium and arsenic simultaneously, the iron-manganese modified sepiolite, the ferrous sulfate modified sepiolite FP (2+), the ferric nitrate modified sepiolite FP (3+), and the zero-valent iron modified sepiolite FP (0).
Example 6 comparison of the effects of adsorbing cadmium and arsenic between iron nitrate-potassium permanganate-modified sepiolite and ferrous sulfate-potassium permanganate-modified sepiolite
(1) The preparation method of the sepiolite modified by the ferrous sulfate and the potassium permanganate comprises the following steps: obtaining iron and manganese modified sepiolite FMP (2+) by the same way as the embodiment 1;
(2) the preparation method of the iron nitrate-potassium permanganate modified sepiolite comprises the following steps: weighing 216g of ferric nitrate nonahydrate and 28g of potassium permanganate, putting into a container, adding water for dissolving, carrying out other steps to implement the embodiment 1, drying the material, and grinding to obtain iron-manganese modified sepiolite FMP (3 +);
the experimental method for measuring the effect of adsorbing cadmium and arsenic in wastewater by using the two kinds of iron-manganese modified sepiolite is the same as the embodiment 1. The adsorption effect of the material prepared by the embodiment on cadmium and arsenic under the laboratory condition is shown in fig. 5, the efficiency of adsorbing cadmium of the iron-manganese modified sepiolite FMP (2+) after 12 hours is 81%, and the efficiency of adsorbing arsenic is 91%; the efficiency of adsorbing cadmium of the iron-manganese modified sepiolite FMP (3+) after 12 hours is 71 percent, and the efficiency of adsorbing arsenic is 79 percent. Therefore, the adsorption effect of the ferrous sulfate and potassium permanganate modified sepiolite on cadmium and arsenic is better than that of ferric nitrate and potassium permanganate modified sepiolite.
Example 7 comparison of the effects of adsorption of cadmium and arsenic by iron-manganese modified clay minerals (sepiolite, bentonite, diatomaceous earth) (1) preparation of iron-manganese modified sepiolite: obtaining iron and manganese modified sepiolite FMP (2+) by the same way as the embodiment 1;
(2) the preparation method of the ferro-manganese modified bentonite comprises the following steps: weighing 200g of bentonite, and obtaining iron-manganese modified bentonite FMB by the same steps as in embodiment 1;
(3) the preparation method of the ferro-manganese modified diatomite comprises the following steps: weighing 200g of diatomite, and obtaining iron-manganese modified bentonite FMS by the same steps as in embodiment 1;
the experimental method for determining the effect of adsorbing cadmium and arsenic in wastewater by using the iron-manganese modified clay mineral is the same as that of embodiment 1. The adsorption effect of the material prepared by the embodiment on cadmium and arsenic under the laboratory condition is shown in fig. 6, the efficiency of adsorbing cadmium by using the iron-manganese modified sepiolite FMP (2+) after 12 hours is 81%, and the efficiency of adsorbing arsenic is 91%; the cadmium adsorption efficiency of the ferro-manganese modified bentonite after 12 hours is 50%, and the arsenic adsorption efficiency is 50%; the efficiency of adsorbing cadmium by using the ferro-manganese modified diatomite after 12 hours is 30%, and the efficiency of adsorbing arsenic is 40%. Therefore, the three ferro-manganese modified clay minerals have the effect of simultaneously adsorbing cadmium and arsenic in the water body, but the ferro-manganese modified sepiolite has the best effect of simultaneously adsorbing cadmium and arsenic.